Energy, Energy Transformations

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energies, the atoms can absorb or release energy

only in these amounts (quanta)

Electron gets energy, jumps to an excited state,

release the energy, and falls back down

The energy is emitted as a photon of light

The photon has exactly the same energy that

the electron has lost

Slide 19

Types of Spectra

Emission line spectrum consists of photons emitted as each electron falls back to lower levels

Absorption line spectrum appears when photons

are absorbed, causing electrons to jump up in energy

Each element or molecule produces its own distinct

set of spectral lines

Slide 20

Emission by Hydrogen

Slide 21

Hydrogen lines in the visible

Slide 22

Examples of Spectra

Slide 23

Thermal Radiation

``Complex’’ objects - planets, stars, people -

produce thermal radiation

Its spectrum depends only on the object’s

temperature

Hotter objects emit more total radiation per unit surface area

The radiated energy is proportional to the fourth power of the temperature

Hotter objects emit photons with a higher average energy

Slide 24

Temperature and Color

Slide 25

Temperature and Intensity

Slide 26

Reflected light

When the light (for example, sunlight) strikes an

object (ground, clouds, people), we see only the

wavelengths of light that are reflected

Different objects (fruits, rocks, atmospheric gases)

reflect and absorb light at different wavelengths

Slide 27

The Doppler Shift

Radial motion of a distant object can be determined due to the Doppler effect

The Doppler effect causes shifts in the wavelengths

of light

If an object is moving toward us, its entire spectrum is shifted to shorter wavelengths

Because shorter wavelengths of the visible light are bluer, the Doppler shift of this object is called a blueshift

The Doppler shift of a moving away object - redshift

Slide 28

Doppler Effect

Demo Doppler effect

Slide 29

Summary